Control circuitry and method for controlling a bi-directional switch system, a bi-directional switch, a switching matrix and a medical stimulator

ABSTRACT

A control circuitry ( 134 ) and a method for controlling a bi-directional switch ( 132 ) is provided. The bi-directional switch ( 132 ) having a control terminal ( 130 ) for receiving a control voltage ( 124 ) to control an on state and an off state of the bi-directional switch ( 132 ) and at least one semiconductor switch in a bi-directional main current path. The control circuitry ( 134 ) comprises an energy storage element ( 102 ), a coupling means ( 101 ) to couple the energy storage element ( 102 ) to a supply voltage to charge the energy storage element ( 102 ), and a control circuit ( 108 ) configured to receive power from the energy storage element ( 102 ) and pendent of the supply voltage when the emergency storage element ( 102 ) is not coupled to the supply voltage. The coupling means ( 101 ) is configured for only coupling the energy storage element ( 102 ) to the supply voltage when the bi-directional switch ( 132 ) is in the off state.

This application is a continuation of U.S. patent application Ser. No.13/636,137 by Blanken et al., filed Sep. 20, 2012, and entitled “ControlCircuitry and Method for Controlling a Bi-Directional Switch System, ABi-Directional Switch, A Switching Matrix And A Medical Stimulator,”which is a 371 National Stage of Patent Cooperation Treaty (PCT)Application No. PCT/IB2011/51456 by Blanken et al., filed on Apr. 5,2011 and entitled “CONTROL CIRCUITRY AND METHOD FOR CONTROLLING ABI-DIRECTIONAL SWITCH SYSTEM, A BI-DIRECTIONAL SWITCH, A SWITCHINGMATRIX AND A MEDICAL STIMULATOR,” and which claims priority fromEuropean Patent Application No. 20100159612.0 by Blanken et al., filedApr. 12, 2010 and entitled “CONTROL CIRCUITRY AND METHOD FOR CONTROLLINGA BI-DIRECTIONAL SWITCH SYSTEM, A BI-DIRECTIONAL SWITCH, A SWITCHINGMATRIX AND A MEDICAL STIMULATOR,” the entire content of each of which isincorporated herein by reference.

FIELD OF THE INVENTION

The invention relates o the field of control circuitry for bidirectionalswitches.

BACKGROUND OF THE INVENTION

In the area of medical stimulators, there is a trend towards anincreased number of stimulation electrode sites to improve therapeuticefficacy by accurate stimulation of the intended target volume usingfield steering. Besides stimulation, there is an increased demand foraccurate sensing of neural activity. Both trends require the presence ofa relatively large cross-point switch matrix to couple stimulationand/or sensing electronics to selected probe electrode sites. Theavailable volume for energy storage is decreasing in thestate-of-the-art medical stimulators, although the required energy forbrain stimulation is substantially constant. Consequently, there is lessroom for a battery, and, thus, the circuitry of medical stimulator hasto be a low power circuitry. The high number of switches of across-point switch matrix imposes an extremely-low power consumptionrequirement on a single switch with its control electronics.

The low-power requirement calls for integrated CMOS switches in ahigh-voltage IC technology, offering isolated NMOS and PMOS transistors.In state-of-the-art high-voltage IC technologies, the driving voltage ofCMOS switches—the gate-to-source voltage—is limited to a few volts incomparison to the much higher voltage that is allowed across the CMOSswitch itself—the drain-to-source voltage.

The article of W. N Reining, “A High voltage cross-point switch formedical applications”, Digest of the 1999 IEEE Southwest Symposium onMixed-Signal Design SSMSD '99, Tucson, Ariz., USA, Apr. 11-13, 1999, pp.109-112, discloses in FIG. 2 a bidirectional switch and a controlcircuit for the bidirectional switch for medical applications, such asmedical stimulators. Two NMOS transistors M10, M11 of which the gatesand the sources are coupled to each other form the bidirectional switch.

A current source, built with a high-voltage PMOS transistor M2, isconnected between the common gate of the bidirectional switch transistorand a voltage supply terminal VH1 which receives a voltage that ishigher than ever is appearing at the bidirectional switch I/O terminals.To turn the bidirectional switch on, the current source M2 is conductinga small current, according to the article 3 μA. The current is conductedby a string of diode-connected NMOS transistors M4, M5, M6 and a highvoltage PMOS transistor M9. The gate of M9 is connected to the commonsource of the bidirectional switch and the drain is connected to avoltage supply terminal VSS which receives a voltage that is at avoltage lower than ever is appearing at the I/O terminals of thebidirectional switch. The voltage drops across the forward-biaseddiode-connected transistors M4, M5 and M6 and the gate-source voltage ofM9, several volts, switch the bidirectional switch to the on-state. Itis to be noted that, when the bidirectional switch is in the on-state,the circuit dissipates an amount of power which is the product of thevalue of the current times the voltage difference between the voltageson the terminals VSS and VHI.

A second current source is built with high-voltage NMOS transistor M8and is connected between the common gate of the bidirectional switchtransistors M10 and M11 and the voltage supply terminal VSS. To controlthe bidirectional switch to be in the off state, the current sourcebuilt with M8 is conducting a small current, which is also conductedthrough high voltage NMOS transistor M3. The gate of M3 is connected tothe common source of the bidirectional switch and the drain is connectedto the voltage supply terminal VH1. The voltage drop between the gateand the source of M3 switches the bidirectional switch in the off state.If the bidirectional switch is in the off state, an amount of power isdissipated that equals the value of the current times the voltagedifference between the voltages on the terminals VSS and VHI.

Thus, the control circuit of the bidirectional switch of the citedarticles has a static power dissipation and the dissipation isirrespective of the state of the bidirectional switch.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a control circuitry for abidirectional switch which consumes less power than the knowncontrolling circuitries.

A first aspect of the invention provides a control circuitry forcontrolling a bi-directional switch as claimed in claim 1. A secondaspect of the invention provides a bi-directional switch system asclaimed in claim 10. A third aspect of the invention provides aswitching matrix as claimed claim 13. A fourth aspect of the inventionprovides a medical stimulator as claimed in claim 14. A fifth aspect ofthe invention provides a method of controlling a bi-directional switchas claimed in claim 15. Advantageous of embodiments are defined in thedependent claims.

A control circuitry for controlling a bi-directional switch inaccordance with the first aspect of the invention comprises an energystorage element, a coupling means and a control circuit. Thebi-directional switch has a control terminal for receiving a controlvoltage to control an on state and an off state of the bi-directionalswitch and has at least one semiconductor switch in a bi-directionalmain current path. The coupling means couples the energy storage elementto a supply voltage for charging energy storage element. The energystorage element is only coupled to the supply voltage when thebi-directional switch is in the off state. The control circuit receivespower from the energy storage element and supplies the control voltagehaving a voltage level being independent of the supply voltage when theenergy storage element not coupled to the supply voltage.

The control circuit receives power from the energy storage element and,thus, the control circuit is able to generate a control voltage which isrelated to the voltage across the energy storage element. Thebi-directional switch receives the control voltage on the controlterminal. To reliably switch on or switch bi-directional switch, thecontrol voltage needs to have a voltage in specific voltage ranges,which is not directly related to supply voltage. When the energy storageelement is not coupled to the supply voltage, the control circuit isable to generate the control voltage which does not directly relate tothe supply voltage, because the voltages of the terminals of the energystorage element may float to required voltage levels. However, when theenergy storage element is being charged, the voltages of the terminalsof the energy storage element become connected to fixed voltage levels,which may prevent the control circuit of generating a control voltagewhich may reliably switch the bi-directional switch on or off.Consequently, the energy storage element is only charged when thebi-directional switch is in the off state.

It is to be noted that the bi-directional switch mainly forms acapacitive load to the control circuitry because the load is formed by agate of at least one semiconductor switch which has to be charged ordischarged to switch from the conducting non-conducting state or viceversa. Thus, the bi-directional switch does not form a static power loadfor the control circuitry.

The coupling means and the control circuit may be implemented as a lowpower semiconductor circuit which only consumes power at the instants atwhich the transistors of the semiconductor circuitry switch to anotherstate. The obtaining of the control voltage does not rely on currentsthat flow permanently. Thus, the control circuitry does not have astatic power consumption.

The control circuitry does not have a static power consumption and thebi-directional switch does not statically consume power via the controlterminal. Hence, the invention according to the first aspect is morepower efficiently than the known circuitries.

In an embodiment, the bi-directional switch further has at least onesemiconductor switch in a bi-directional main current path and areference voltage output terminal for providing a reference voltageindicating to which voltage level the control voltage on the controlterminal has to be defined to enable switching of the bi-directionalswitch. The control circuitry further comprises a reference voltageinput terminal for receiving the reference voltage from the referencevoltage output terminal. The energy storage element has a first terminaland a second terminal. The coupling means comprises a first switcharranged between the first terminal and a first supply voltage terminalto receive a first supply voltage, a second switch arranged between thesecond terminal and a second supply voltage terminal to receive a secondsupply voltage, and a further control circuit. The further controlcircuit controls at least one of the first switch and the second switchto be open or closed and only closes at least one of the first switchand the second switch when the bi-directional main current path of thebi-directional switch is in the off state. When both the first switchand the second switch are closed, the energy storage element is chargedto a voltage being a difference between the first supply voltage and thesecond supply voltage. When both the first switch and the second switchare open, the voltages of the first terminal and the second terminal arefloating to obtain a floating state of the energy storage element. Thecontrol circuit comprises power supply terminals that are coupledbetween the first terminal and the second terminal to receive powersupply energy from the energy storage element. The control voltage isgenerated in a floating manner when the energy storage element is in thefloating state.

The control circuit receives a supply voltage from the first terminaland the second terminal and, thus, the control circuit is able togenerate a control voltage which is directly related to the voltage ofthe first terminal or the voltage of the second terminal. The controlvoltage may have a value in a range limited by the voltage of the firstterminal and the voltage of the second terminal. When the energy storageelement is in the floating state, the control voltage floats as well.

The bi-directional switch has at least one semiconductor switch in themain current path. Such a semiconductor switch can only be closed when acontrol voltage is received which is high enough, or low enough,compared to the reference voltage. In an embodiment, the referencevoltage input terminal may be coupled to the second terminal, thus, whenthe energy storage element is in the floating state, the referencevoltage determines the voltage level of the second terminal, andconsequently, the level of the first terminal. Thus, if the controlcircuitry receives the reference voltage, the control circuit is able togenerate the control voltage with respect to the reference voltage suchthat the bi-directional switch may be opened or closed independently ofthe first supply voltage and the second supply voltage which are used tocharge the energy storage element. In another embodiment, the referencevoltage input terminal may be coupled to the control circuit such thatthe control circuit may directly generate the control voltage withrespect to the voltage level of the reference voltage.

It is to be noted that the bi-directional switch forms mainly acapacitive load to the control circuitry because the load is formed by agate of the at least one semiconductor switch which has to be charged ordischarged to switch from the conducting to the non-conducting state orvice versa. Thus, the bi-directional switch does not form a static powerload for the control circuitry. Only when the bi-directional switch isin the on state, a current flows through the bi-directional main currentpath which may result in a small power dissipation in the main currentpath. However, this power dissipation in the main current path is not aload for the control terminal, because the control terminal only needsto charge or discharge the gate of the at least one semiconductorswitch. Changing the state of the bi-directional switch from theconductive to the non-conductive state and/or vice versa leads to powerdissipation in the control circuit during the transition. Thiswell-known dynamic power dissipation can not be avoided. The energyrequired is taken from the energy stored in the energy storage element.

The control circuit operates on basis of supply power received from theenergy storage element. In order to store energy in the energy storageelement and to obtain a voltage across the energy storage element, theenergy storage element has to be charged. By connecting the firstterminal and the second terminal via the first switch and the secondswitch to the first supply voltage terminal and the second supplyvoltage terminal, respectively, energy is stored in the energy storageelement. When the first switch and/or the second switch are closed, thevoltage of the first terminal and the voltage of the second terminal donot float anymore and the control voltage is not generated in thefloating manner. The non-floating control voltage can not reliableswitch the at least one semiconductor switch of the bi-directionalswitch, and, thus, the charging of the energy storage element may onlybe performed when the bi-directional switch is in the off state.

The further control circuit and the control circuit may be implementedas a low power semiconductor circuit which only consumes power at theinstants at which the transistors of the semiconductor circuitry switchto another state. The obtaining of the control voltage does not rely oncurrents that flow permanently. Thus, the control circuitry does nothave static power consumption.

The control circuitry does not have a static power consumption and thebi-directional switch does not statically consume power via the controlterminal. Hence, the invention according to the first aspect is morepower efficient than the known circuitries.

In an embodiment the bi-directional switch is always open in apredefined time period of iterating cycles. This knowledge may be usedby the further control circuit to close the first switch and the secondswitch during the interval of which is a-priori known that thebi-directional switch is not closed.

In another embodiment, the further control circuit is coupled to thecontrol circuit for receiving an indication whether the bi-directionalswitch is in the off-state. On basis of the received indication thefurther control circuit may decide whether the first switch and thesecond switch may be closed or not.

In another embodiment, the control circuit comprises a latch. The latchmemorizes the on state or the off state of the bi-directional switch andsupplies the control voltage according to the memorized state.

It is advantageous to have a latch which memorizes the on or off stateof the bi-directional switch, because it does not require the continuousreceiving of a signal which indicates the on or the off state. Such asignal with on/off information may be provided for a limited time periodand subsequently the latch memorizes the provided information.Especially it prevents the discharging of the energy storage elementwhen the bi-directional switch is switched to the off state because thebi-directional switch is decoupled from the energy storage element. Thisincreases power efficiency.

In an embodiment, the control circuit comprises an input terminal forreceiving a switch control signal which indicates a required on or offstate of the bi-directional switch. In other words, the received switchcontrol signal is used by the control circuit to generate the controlvoltage such that the bi-directional switch opens or closes as indicatedby the switch control signal. Other circuitry, for example, somecircuitry of an apparatus which comprises the control circuitryaccording to the invention, may generate the switch control signal.

In a further embodiment, the control circuit is coupled to the firstsupply voltage terminal and/or the second supply voltage terminal. Theinput terminal is configured to receive the switch control signal whichrelates to at least one of the first supply voltage and the secondsupply voltage. The control circuit further comprises a communicationchannel circuit to communicate the switch control signal to a floatingcontrol signal having a voltage related to the voltage of the firstterminal and/or the second terminal.

In other words, the provided switch control signal is not a floatingvoltage and is, for example, a voltage in a voltage range limited by thefirst supply voltage and the second supply voltage. Such a switchcontrol signal may be received from a circuitry which receives powerfrom the first supply voltage and the second supply voltage. The voltageof the provided switch control signal has to be translated into avoltage which is directly related to the floating voltage, for example,to a voltage in a voltage range limited by the voltage of the firstterminal and the voltage of the second terminal. The communicationchannel circuit performs the translation. The translation has to beperformed because the control signal is also related to the floatingvoltages of the first terminal and/or the second terminal. To performthe translation, the control circuit may receive the first supplyvoltage and/or the second supply voltage such that the communicationchannel may determine how the received switch control signal exactlyrelates to the first supply voltage and/or the second supply voltage. Itis to be noted that the function of the communication channel is thelevel-shifting of the switch control signal to another level and thatthis function does not necessarily require a connection to the firstsupply voltage terminal and/or the second supply voltage terminal. Inother embodiments the communication channel is connected to terminalswhich have a fixed voltage different from the first supply voltageterminal and/or the second supply voltage terminal.

The embodiment is advantageous because it allows the receiving of abi-directional switch control signal that is related to the first supplyvoltage and/or the second supply voltage which means that a circuitrywhich provides this signal does not have to be aware of the floatingvoltages in the control circuitry. The control circuit may compare thereceived bi-directional switch control signal with the first supplyvoltage and/or the second supply voltage to interpret the bi-directionalswitch control signal. In an example, the bi-directional control signalmay substantially equal the first voltage to indicate that thebi-directional switch has to be in the on state, and may substantiallyequal the second voltage to indicate that that the bi-directional switchhas to be in the off state.

In a further embodiment, the latch of the control circuit stores the onstate of the bi-directional switch in response to receiving a set signaland stores the off state of the bi-directional switch in response toreceiving a reset signal. The bi-directional switch control signalcomprises a set sub-signal and a reset sub-signal. The communicationchannel circuit communicates both the set sub-signal and the resetsub-signal to the latch.

With the use of a set and a reset signal, the setting of the state ofthe latch requires only temporarily a signal in the form of a set signalor a reset signal. Because of the limitation in time, the communicationchannel circuit only has to perform the translation from a voltagerelated to the first supply voltage and/or the second supply voltagetowards a voltage related to the voltage of the first terminal and/orthe voltage of the second terminal during limited time periods. Thus,the communication channel circuit consumes a limited amount of power andthe power efficiency of the control circuitry is increased.

In another embodiment, the energy storage element is a storage capacitorwhich is manufactured on basis of a MOS transistor of which the drain,the source and the backgate are electrically connected to each other andform together a first electrode of the storage capacitor, and the gateof the MOS transistor forms the second electrode of the capacitor.

In other words, the gate oxide of a MOS transistor is used as thedielectric of the storage capacitor. Using the gate oxide as thedielectric is advantageous because it allows the integration of thestorage capacitor in a semiconductor technology, and prevents the use ofan external storage capacitor which has to be connected to the circuitryby means of external ports.

The storage capacitor has to store a small amount of energy which isenough to open and/or close the bi-directional switch once or multipletimes in between the time intervals during which the storage capacitoris charged. It is expected that, when the storage capacitor is alwayscharged when the bi-directional switch is open, the storage capacitorhas only to store energy which is enough for closing and subsequentlyopening the bi-directional switch only once. Thus, the amount of storedenergy is relatively small and thus the size of the storage capacitormay be relatively small which is advantageous in the context ofintegrating the storage capacitor in the semiconductor technology.However, the capacitor may be constructed in another suitable manner.

In an embodiment, the first switch or the second switch is a bootstrapdiode, and the other one of the first switch and the second switch is aMOS transistor. The conducting or non-conducting state of the MOStransistor is controlled by the further control circuit.

The bootstrap diode has to be connected between the first terminal andthe first supply voltage terminal, or between the second terminal andthe second supply voltage terminal such that the bootstrap diode cannotconduct a current when the energy storage element is in the floatingstate and that it can conduct the current when the energy storageelement is not in the floating state. Only when the voltage of the firstterminal is connected via a conducting MOS transistor to the firstsupply voltage, or when the voltage of the second terminal is connectedvia a conducting MOS transistor to the second supply voltage, the energystorage element is not in the floating state, and, thus, the energystorage element receives energy via the MOS transistor and via thebootstrap diode. The use of one MOS transistor and one bootstrap diodeis an efficient solution because the diode is a relatively cheap andrelatively simple component. It is to be noted that the bootstrap diodeis not an active switch, but acts as a passive switch which becomesconducting when the voltage across the diode (the anode—cathode voltage)is larger than the (forward) threshold voltage of the diode. If thefirst switch and the second switch are implemented according to thisembodiment, the further control circuit only directly controls the MOStransistor to be in the on state and thereby indirectly controls theother switch, implemented as the bootstrap diode.

In another embodiment, the first switch is a first MOS transistor andthe second switch is a second MOS transistor. The further controlcircuit controls a conducting or a non-conducting state of the first MOStransistor as well as a conducting or a non-conducting state of thesecond MOS transistor.

The use of two MOS transistors is an efficient and effective solutionfor creating the first switch and the second switch and provides fullcontrol with respect to the floating or non-floating state of the energystorage element and with respect to the charging of the energy storageelement and also avoids the voltage drop of a forward-biased diode, whenthe switch is, for example, implemented as a bootstrap diode. Thus, iftwo MOS transistors are used, the energy storage element may be chargedto a voltage level which is substantially equal to the differencevoltage of the first supply voltage and the second supply voltage.

In accordance to the second aspect of the invention, a bi-directionalswitch system is provided which comprises a bi-directional switch andthe control circuitry according to the first aspect of the invention.The bi-directional switch provides the same benefits as the controlcircuitry according to the first aspect of the invention and has similarembodiments with similar effects as the corresponding embodiments.

In an embodiment, the bi-directional switch comprises a main currentpath between a first I/O terminal and a second I/O terminal and furthercomprises a first MOS transistor and a second MOS transistor in the maincurrent path. The first MOS transistor and the second MOS transistorhave a common source and a common gate. A drain of the first MOStransistor is coupled to the first I/O terminal and a drain of thesecond MOS transistor is coupled to the second I/O terminal. The commongate is coupled to the control terminal.

Using two MOS transistors in the main current path of a bi-directionalswitch is an effective and efficient solution by which the main currentpath may be opened or closed.

In an embodiment the common source is coupled to the reference voltageoutput terminal of the bi-directional switch.

Thus, when the energy storage element is in the floating state, thefloating voltage of the second terminal follows the voltage of thecommon source of the first MOS transistor and the second MOS transistor.Especially when the bi-directional switch is in the on state, thevoltage of the common source is in a range which is limited by thevoltage of the first I/O terminal and the voltage of the second I/Oterminal. Thus, when, for example, a sinus signal is transmitted throughthe bi-directional switch, the voltages of the first I/O terminal andthe second I/O terminal are continuously varying, and, consequently, thevoltage of the common source varies accordingly, as well as the floatingvoltage of the second terminal. The voltage of the first terminal isrelated to the voltage of the second terminal via the energy storageelement, and consequently varies also according to the voltage of thecommon source as well. Thus, the control voltage that is generated bythe control circuit may be used to switch the first MOS transistor andthe second MOS transistor in the off or the on state because thegenerated control voltage relates to the voltage of the common source.

According to a third aspect of the invention, a switching matrix isprovided which comprises at least one bi-directional switch systemaccording to the second aspect of the invention at at least one junctionpoint of the matrix. Such a switching matrix, for example, may be across-point matrix used to couple electrodes of a medical stimulator tosignal generators and/or measurement circuits.

According to a fourth aspect of the invention, a medical stimulator isprovided which comprises at least one bi-directional switch systemaccording to the second aspect of the invention.

The switching matrix and the medical stimulator provide the samebenefits as the bi-directional switch according to the second aspect ofthe invention and have similar embodiments with similar effects as thecorresponding embodiments.

According to a fifth aspect of the invention, a method of controlling abi-directional switch is provided. The bi-directional switch has acontrol terminal for receiving a control voltage to control an on andoff state of the bi-directional switch and at least one semiconductorswitch in a bi-directional main current path. The method comprises afirst step of coupling an energy storage element to a supply voltageonly when the bi-directional switch is in the off state for charging theenergy storage element. In another step the method receives power fromthe energy storage element. In a further step the method supplies thecontrol voltage having a voltage level being independent of the supplyvoltage when the energy storage element is not coupled to the supplyvoltage.

The method according to the fifth aspect of the invention provides thesame benefits as the control circuitry according to the first aspect ofthe invention and has similar embodiments with similar effects as thecorresponding embodiments of the circuitry.

In an embodiment of the method of controlling the bi-directional switch,the bi-directional switch has at least one semiconductor switch in abi-directional main current path, a control terminal to control an onand off state of the bi-directional main current path, and a referencevoltage output terminal for providing a reference voltage indicating towhich voltage level a signal on the control terminal has to relate. Themethod comprises a first step of receiving a first supply voltage at afirst supply voltage terminal and receiving a second supply voltage at asecond supply voltage terminal. The method comprises a further step ofcontrolling by means of a first control circuit a first switch and asecond switch both to be closed only when the bi-directional switch isin the off state. The first switch is arranged between the first supplyvoltage terminal and a first terminal of an energy storage element andthe second switch is arranged between the second supply voltage terminaland a second terminal of the energy storage element. The methodcomprises another step of controlling by means of the first controlcircuit the first switch and the second switch both to be open to obtainthe energy storage element in a floating state. The method comprises afurther step of receiving the reference voltage of the bi-directionalswitch at a reference voltage terminal which is coupled to the secondterminal. The method comprises also the step of receiving the voltage ofthe first terminal and the second terminal at power supply terminals ofa second control circuit. And the method comprises the step ofgenerating a control voltage at an output terminal of the second controlcircuit. The output terminal is coupled to the control terminal of thebi-directional switch. The control voltage is generated in a floatingmanner when the energy storage element is in a floating state.

These and other aspects of the invention are apparent from and will beelucidated with reference to the embodiments described hereinafter.

It will be appreciated by those skilled in the art that two or more ofthe above-mentioned embodiments, implementations, and/or aspects of theinvention may be combined in any way deemed useful.

Modifications and variations of the system, and/or of the method whichcorrespond to the described modifications and variations of the system,can be carried out by a person skilled in the art on the basis of thepresent description.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 a schematically shows an embodiment of the control circuitryaccording to the first aspect of the invention,

FIG. 1 b schematically shows another embodiment of the control circuitryaccording to the first aspect of the invention,

FIG. 2 a schematically shows an embodiment of the control circuitry andof the bi-directional switch wherein the bi-directional switch comprisestwo NMOS transistors,

FIG. 2 b schematically shows an embodiment of the control circuitry andof the bi-directional switch wherein the bi-directional switch comprisestwo PMOS transistors,

FIG. 3 schematically shows two embodiments of an energy storage element,

FIG. 4 a schematically shows an embodiment of the first switch and ofthe second switch,

FIG. 4 b schematically shows another embodiment of the first switch andof the second switch,

FIG. 5 a schematically shows a first embodiment of a communicationchannel,

FIG. 5 b schematically shows a second embodiment of a communicationchannel,

FIG. 6 a schematically shows a third embodiment of a communicationchannel,

FIG. 6 b schematically shows a fourth embodiment of a communicationchannel,

FIG. 6 c schematically shows a fifth embodiment of a communicationchannel,

FIG. 7 a schematically shows a circuit of a latch and a circuit which iscoupled in between the latch and a communication channel,

FIG. 7 b schematically shows another circuit of a latch and anothercircuit which is coupled in between the latch and a communicationchannel,

FIG. 8 schematically shows an additional circuit which may be coupledbetween a latch and the bi-directional switch,

FIG. 9 schematically shows another embodiment of the bi-directionalswitch,

FIG. 10 schematically shows the embodiment of FIG. 9 inclusive parasiticdiodes,

FIG. 11 schematically shows an embodiment of a bi-directional switchaccording to the second aspect of the invention,

FIG. 12 schematically shows an embodiment of a switching matrixaccording to the third aspect of the invention,

FIG. 13 schematically shows an embodiment of a medical stimulatoraccording to the fourth aspect of the invention, and

FIG. 14 schematically shows an embodiment of a method according to thefifth aspect of the invention.

It should be noted that items denoted by the same reference numerals indifferent Figures have the same structural features and the samefunctions, or are the same signals. Where the function and/or structureof such an item have been explained, there is no necessity for repeatedexplanation thereof in the detailed description.

The figures are purely diagrammatic and not drawn to scale. Particularlyfor clarity, some dimensions are exaggerated strongly.

DETAILED DESCRIPTION OF THE EMBODIMENTS

A first embodiment is shown in FIG. 1 a. A control circuitry 134 forcontrolling a bi-directional switch 132 is shown. The bi-directionalswitch 132 comprises a control terminal 130 to receive a control voltage124 to control an on state and an off state of the bi-directional switch132. The control circuitry 134 comprises an energy storage element 102,a coupling means 101 and a control circuit 108. The coupling means 101couples the energy storage element 102 to a supply voltage V_(sup) tocharge the energy storage element 102. The coupling means 101 onlycouples the energy storage element 102 to the supply voltage V_(sup)when the bi-directional switch 132 is in the off state. The controlcircuit 108 receives power from the energy storage element 102 andsupplies the control voltage 124 which has a voltage level that isindependent of the supply voltage V_(sup) when the energy storageelement 102 is not coupled to the supply voltage V_(sup).

Another embodiment is shown in FIG. 1 b. A schematic drawing of anembodiment of a control circuit 134 is shown which is connected to abi-directional switch 132 which is also drawn schematically. Thebi-directional switch 132 has a bi-directional main current path 144between a first I/O terminal 140 and a second I/O terminal 146. At leastone controllable semiconductor switch 143 is provided in thebi-directional main current path 144. The bi-directional switch 132 as acontrol terminal 130 for controlling an on state and an off state of thebi-directional main current path 144. The bi-directional switch 132 hasfurther a reference voltage output terminal 142 for providing areference voltage 128 which indicates to which voltage level a receivedcontrol voltage on the control terminal 130 has to be defined to enableswitching of the bi-directional switch. Thus, depending on the voltagedifference between the reference voltage and the control voltagereceived at the control terminal 130, the bi-directional switch 132 iscontrolled in the on or in the off state.

The control circuitry 134 comprises a first supply voltage terminal 112for receiving a first supply voltage and has a second supply voltageterminal 120 for receiving a second supply voltage. The controlcircuitry 134 further comprises an energy storage element 102 having afirst terminal 104 and a second terminal 136. A first switch 114 isarranged between the first supply voltage terminal 112 and the firstterminal 104. A second switch 118 is arranged between the second supplyvoltage terminal 120 and the second terminal 136. The control circuitry134 further comprises a further control circuit 116 which controls thefirst switch 114 and the second switch 118 to be open or closed. Whenboth the first switch 114 and the second switch 118 are closed theenergy storage element 102 is charged to a voltage being a differencevoltage between the first supply voltage and the second supply voltage.When both the first switch 114 and the second switch 118 are open, thevoltages of the first terminal 104 and the second terminal 136 arefloating and consequently a floating state of the energy storage element102 is obtained.

The control circuitry 134 further comprises a control circuit 108 forgenerating a control voltage 124 at an output terminal 110 of thecontrol circuit 108. The control voltage 124 is supplied to the controlterminal 130 of the bi-directional switch. The control circuit 108 haspower supply terminals 106, 138 to receive power supply energy from theenergy storage element 102. Thus, power supply terminal 106 is coupledto the first terminal 104 and power supply terminal 138 is coupled tothe second terminal 136. The control voltage 124 is generated in afloating manner when the energy storage element 102 is in the floatingstate. Thus, the generated control voltage 124 relates to the voltage ofthe first terminal 104 and/or of the second terminal 136. In an example,the voltage level of the control voltage 124 is in a range that islimited by the voltage of the first terminal 104 and the voltage of thesecond terminal 136.

The control circuitry 134 further has a reference voltage input terminal126. The reference voltage input terminal 126 receives a referencevoltage 128 from the reference voltage output terminal 142.

In an embodiment, the reference voltage terminal is coupled to thecontrol circuit 108 such that the control circuit 108 may generate thecontrol voltage 124 which is defined with respect to the receivedreference voltage 128

In another embodiment, the reference voltage terminal is coupled to thesecond terminal 136. Thus, if the energy storage element 102 is in thefloating state, the received reference voltage 128 determines thevoltage of the second terminal 136. Subsequently, the energy storageelement 102 determines the voltage difference between the first terminal104 and the second terminal 136, and thus, the voltage of the firstterminal 104 relates also to the reference voltage 128 if the energystorage element 102 is in the floating state. The control circuit 108receives at its power supply terminals 106, 138 the voltages of thefirst terminal 104 and the second terminal 136, and, consequently, thegenerated control voltage 124 primarily relates to the voltages of thefirst terminal 104 and the second terminal 136, and thus, the generatedcontrol voltage 124 is defined with respect to the reference voltage128. When the energy storage element 102 is in the floating state, thevoltage difference between the reference voltage 128 and the controlvoltage 124 determines the on or off state of the bi-directional switch132.

The further control circuit 116 of the control circuitry 134 only closesthe first switch 114 and/or the second switch 118 when the main currentpath 144 of the bi-directional switch 132 is in the off state. If thefirst switch 114 or the second switch 118 is closed, the voltage of thefirst terminal 104 or the second terminal 136, respectively, is notfloating anymore. This means that the generated control voltage 124 doesnot float anymore. The bi-directional switch 132 can only be closedreliably when the received control voltages 124 relates to the referencevoltage 128 and not to the fixed first supply voltage or the fixedsecond supply voltage. Thus, the first switch 114 and/or the secondswitch 118 may only be closed when the bi-directional switch 132 is inthe off state. In order to charge the energy storage element 102, boththe first switch 114 and the second switch 118 have to be closed.

The further control circuit 116 may have predefined knowledge about thetime intervals during which the bi-directional switch 132 is in the offstate. The bi-directional switch 132 may be open during predefinedintervals of iterating cycles and as such the further control circuit116 may close the first switch 114 and/or the second switch 118 duringthe predefined intervals.

FIG. 2 a schematically shows an embodiment 202 of a control circuitryand a bi-directional switch 212 which may be manufactured in p-typesubstrate semiconductor technology. The bi-directional switch 212 isimplemented with two NMOS transistors M1, M2 which are placed in ananti-series configuration, which means that they have a common gate gand a common source s. A drain d1 of one of the MOS transistors M1, M2is a first I/O terminal of the bi-directional switch 212 and a drain d2of the other one of the MOS transistors M1, M2 is a second I/O terminalof the bi-directional switch 212.

The control circuitry comprises a first switch S1, a second switch S2, astorage capacitor C_(stor), a first controller 210 and a secondcontroller 208. A voltage supply E_(energy) provides a first voltage+fixed and a second voltage −fixed which is lower than the first voltage+fixed. The first switch receives the first voltage +fixed and provides,when the first switch S1 is closed, the first voltage +fixed to a firstterminal of the storage capacitor. The voltage of the first terminal isindicated in the figure with +fl. The second switch S2 receives thesecond voltage −fixed and provides, when the second switch S2 is closed,the second voltage −fixed to a second terminal of the storage capacitor.The voltage of the second terminal is indicated in FIG. 2 a with −fl.

When both the switches S1 and S2 are closed, the storage capacitorC_(stor) is charged to obtain, when the storage capacitor C_(stor) iscompletely charged, a voltage difference between the first terminal andthe second terminal of the storage capacitor C_(stor) which issubstantially equal to the voltage of the voltage supply E_(energy).When both the switches S1 and S2 are open, the voltages +fl, −fl of thefirst terminal and of the second terminal, respectively, are floating.It is to be noted that it is not essential that the switches S1 and S2are closed sufficiently long to completely charge the capacitorC_(stor). It is sufficient to charge the capacitor C_(stor) to a voltagelevel which is required for providing the control circuit 206 withsufficient supply power to be able to control the bi-directional switch212.

The second terminal is connected to the common source s of thebi-directional switch 212 and as such the voltage of the common source sand the voltage of the second terminal −fl follow each other. When thebi-directional switch 212 is in the on state the voltage of the commonsource s is in between the voltage of the first I/O terminal d1 and ofthe second I/O terminal d2. At such moments the switches S1 and/or S2may not be closed, otherwise the voltage of the second terminal may bein conflict with the voltage of the common source s. Thus, when thebi-directional switch 212 is in the on state, none of the switches S1and S2 may be closed, and only when the bi-directional switch 212 is inthe off state, the switches S1 and/or S2 may be closed.

The opening and closing of switches S1 and S2 is controlled by a furthercontrol circuit 210. In an embodiment, the bi-directional switch 212 isalways in the off state during predefined intervals of successivecycles, and predefined knowledge of these predefined intervals ofsuccessive cycles may be available in the further control circuit 210such that the further control circuit 210 only closes the switches S1and/or S2 during the predefined intervals.

The control circuitry further comprises the control circuit 208 whichcomprises a communication channel 204 and a latch 206. Both thecommunication channel 204 and the latch 206 receive a power supplyvoltage from the storage capacitor C_(stos). The communication channelis further connected to the second supply voltage −fixed. Thecommunication channel receives an input signal at an input port In whichindicates whether the bi-directional switch has to be in the on state orin the off state. The received input signal has a voltage level whichrelates to the first voltage +fixed and/or relates to the second voltage−fixed, for example, the voltage level of the input signal is in a rangelimited by the first voltage +fixed and by the second voltage −fixed.The communication channel translates the received input signal to anoutput signal of the communication channel which has a voltage levelwhich relates to the voltage level +fl of the first terminal and/or tothe voltage level −fl of the second terminal, for example, a voltagelevel in a range which is limited by the voltage level +fl and thevoltage level −fl. The output signal of the communication channel 204 isused to set or reset the latch 206 to a specific state and the latch 206provides a control voltage to the common gate g according to the stateof the latch 206.

The generated control voltage relates to the voltage level +fl of thefirst terminal and/or the voltage level −fl of the second terminal andbecause the second terminal is coupled to the common source s a desiredcontrol voltage is generated by the latch 206 such that thegate-source-voltage of the NMOS transistors M1 and M2 is such that thebi-directional switch 212 is closed or opened. If the control voltage ishigher than the threshold voltage of the NMOS transistors M1 and M2, thebi-directional switch 212 is in the on-mode. Thus, the latch 206 mayprovide a control voltage which is close to the voltage level +fl of thefirst terminal when the bi-directional switch 212 had to be in the onstate and the latch 206 may provide a control voltage which is close tothe voltage level −fl of the second terminal when the bi-directionalswitch 212 had to be in the off state.

In an embodiment, the further control circuit 210 is coupled to thecontrol circuit 208 to receive an indication when the bi-directionalswitch is controlled to be in an off state. This indication is used bythe further control circuit 210 to decide whether the first switch S1and/or the second switch S2 may be closed or should be open.

In FIG. 2 b another embodiment 214 of the bi-directional switch 220 andof the control circuitry is schematically drawn. The embodiment issimilar to the embodiment of FIG. 2 a, however, the bi-directionalswitch 220 comprises two PMOS transistors M10, M20 and thus the latch224 has to provide a control voltage which the inverse of the controlvoltage of the embodiment of FIG. 2 a, because the bi-directional switch220 is closed when the voltage of a common gate g of the PMOStransistors M10, M20 is lower than the voltage of a common source s ofthe PMOS transistors M10, M20. The first controller 216, the latch 224and the communication channel 218 are similar to the first controller210, the latch 206, and the communication channel 204 of the embodimentof FIG. 2 a.

In FIG. 3 two schematic embodiments of energy storage elements 302, 304are presented. The energy storage element may be implemented as astorage capacitor, which may be manufactured in a semiconductortechnology by means of a NMOS transistor 302 or a PMOS transistor 304.The source s, the drain d and the backgate of both the NMOS transistor302 and the PMOS transistor 304 form a first electrode of the storagecapacitor and the gate g forms the second electrode. Thus, thegate-oxide forms the dielectric of the storage capacitor. Otherembodiments of a storage capacitor implemented in a semiconductortechnology are a so-termed Metal-Insulator-Metal (MIM) capacitor and aso-termed fringe-capacitor. The MIM capacitor is manufactured on basisof a first electrode in one of the standard metal layers of themetal-layer-stack of the semiconductor device, on top of which a thinlayer of an insulating material is deposited whereon a second metalelectrode is manufactured. The fringe-capacitor comprises twointerdigitated electrodes manufactured in one metal layer of thesemiconductor device or manufactured in two or more neighboring metallayers of the semiconductor device. The finger-shaped parts of the firstelectrode form a capacitance together with the finger-shaped parts ofthe second electrode. It is to be noted that the discussed embodimentsof the energy storage elements are meant to be manufactured in asemiconductor technology, which is advantageous in order to obtain asingle device which comprises the complete control circuitry. However,the energy storage element may also be manufactured on a separatesemiconductor device. For example, in a three dimensional semiconductorarrangements, a first semiconductor device may comprise the logic of thecontrol circuitry and may comprise contacts at the top surface of thefirst semiconductor device, and a second semiconductor device which isarranged to be placed on the top surface of the first semiconductordevice comprises the energy storage element. Especially, for example, inswitching matrix semiconductor devices it may be advantageous tomanufacture the energy storage elements in a separate semiconductordevice which is placed on top of a semiconductor device comprising theswitching logic such that larger switching matrices may be manufactured.

In FIG. 4 a a first embodiment 402 of the first switch and the secondswitch is presented. The second switch is formed by an NMOS transistorT_(S2) of which the conducting state is controlled by a further controlcircuit 404. Especially if the second switch is controlled to be in theconducting state, the voltage level −fl of the second terminal becomessubstantially equal to the second supply voltage −fixed. The voltagelevel +fl of the first terminal drops to a level below the first supplyvoltage +fixed, because it is expected that the energy storage elementis not fully charged anymore. The first switch is formed by a bootstrapdiode D_(S1). If the first supply voltage +fixed is higher than thevoltage level +fl of the first terminal, the bootstrap diode becomesconductive and the energy storage element is charged. After a shortperiod of time, apart from the voltage drop across the forward-biaseddiode, the voltage level of the +fl of the first terminal becomessubstantially equal to the first supply voltage +fixed. It is to benoted that the conducting and non-conducting state of the bootstrapdiode is not directly controlled by the further control circuit 404,however, by controlling the second switch to be in the conducting state,the state of the bootstrap diode is indirectly controlled by the furthercontrol circuit 404.

In FIG. 4 b a second embodiment 406 of the first switch and the secondswitch is presented. The first switch and the second switch areimplemented as NMOS transistors T_(S1), T_(S2) of which the conductingor non-conducting state is controlled by a further control circuit 408.When both NMOS transistors T_(S1), T_(S2) are controlled to be in theconducting state the capacitor is charged from the voltage supplyE_(energy).

In FIG. 5 a an embodiment of a communication channel 502 is presented.The signal T₁ctrl is a bi-directional switch control signal that isreceived by the control circuit and indicates a desired on or off stateof the bi-directional switch. The signal T₁ctrl is connected to the gateof NMOS transistor T1. The communication channel further receives thefirst supply voltage −fixed and the voltage +fl of the first terminal.The T₁ctrl signal has a voltage level which relates to the first supplyvoltage −fixed. The output terminal Out of the communication channelprovides a translated bi-directional switch control signal which has avoltage level which relates to the voltage +fl of the first terminal.

The conducting state of transistor T1 is controlled by the T₁ctrlsignal. If transistor T1 does not conduct, the output voltage at theoutput terminal Out is substantially equal to the voltage +fl. If thetransistor T1 conducts, a current flows through the resistor R1 and thetransistor T1, and a voltage drop across resistor R1 determines how muchthe output voltage at the output terminal Out is below the voltage +fl.Thus, the signal of the output terminal Out relates to the floatingvoltage +fl.

The voltage swing of the output terminal Out has to be obtained by anaccurate parameterization of the components of the circuit 502. Thevoltage swing depends on, for example, the threshold voltage of T1, thecurrent gain factor of T1, the resistance of R1, etc.

FIG. 5 b presents another embodiment of a communication channel 504. Inthe embodiment the bi-directional switch control signal which isreceived by the control circuit comprises a set sub-signal InS and areset sub-signal InR. Both signals are translated to a voltage levelwhich relates to the floating voltage +fl with two communication channelsub-circuits which are similar to the embodiment of FIG. 5 a. Set (InS)and Reset (InR) signals are used to set or reset the state of the latch,respectively, and thereby controlling the state of the bi-directionalswitch. To control the state of the latch, the Set (InS) and Reset (InR)signals have only to be provided for a relatively short period of time.Only during the relatively short period of time a current flows throughthe resistors R10, R20 and the transistors T1 and T20. Thus, thecommunication channel only consumes power when the bi-directional switchhas to be switched to another state. Hence, the communication channeldoes not consume static power.

In FIG. 6 a another embodiment of one half the communication channel 602is presented. When a set sub-signal and a reset sub-signal are receivedby the control circuit, the circuit 602 has to be implemented twice,once for translating the set sub-signal to a signal related to thevoltage levels −fl and +fl, and once for translating the resetsub-signal to a signal related to the voltage levels −fl and +fl.

The communication channel 602 is an improved communication channelcompared to the embodiments 502 and 504 of FIG. 5 a and FIG. 5 b,respectively. The communication channel 602 has a better output voltageswing between the floating voltages +fl and −fl of the first terminaland the second terminal respectively. A (high-voltage) PMOS transistorT₂ is added in the branch that links the fixed voltages +fixed and−fixed to the floating voltages +fl and −fl. An input transistor T₁ isnormally switched off. Resistor R₁₁ pulls node Out1 towards the voltagelevel +fl. PMOS transistor T₂ is highly conductive, as its gate is tiedto −fl, so an interconnected drains of T₁ and T₂ also show the +flvoltage. Two inverter stages T₄/T₅ and T₆/T₇ provide a normally-highoutput node Out3, and all three branches do not dissipate. When a gateof the input transistor T₁ is pulled high (implying the reception of aset or reset sub-signal) a conductive channel of T₁ pulls theinterconnected drains of T₁ and T₂ down, and also the Out1 node comesdawn. A resistance of R₁ is chosen such that without T₂ the inputtransistor T₁ would easily pull the Out1 node below the local negativesupply rail −fl. By introducing T₂, this is no longer possible, as T₂would be switched off. The resulting voltage at the Out1 node isslightly above the floating voltage −fl, namely at least a PMOSthreshold voltage. The inverter stage T₄/T₅ now has a relatively lowvoltage at its input, but NMOS T₄ probably will not be switched offcompletely. The widths and lengths of T₄ and T₅ have to be selected suchthat the output node Out2 is pulled high (requiring a relatively weakNMOS T₄ and a relatively strong PMOS T₅). Inverter stage T₆/T₇ creates alogic “low” at the output Out3. As long as T₁ is activated the twoleft-hand branches may dissipate and the inverter stage T₆/T₇ does notshow static dissipation. As noted before, T₁ is only active during therelatively short time intervals during which a set or reset sub-signalis received.

In the embodiment 602 of FIG. 6 a a source-to-backgate junction of PMOStransistor T2 is shorted, which reduces the threshold voltage and thuscreates a voltage of node Out1 relatively close to the floating voltage−fl. However, a disadvantage is the requirement to use an additionalhigh-voltage island in the semiconductor device for T₂, which increasesthe parasitic capacitance to the substrate and decreases thehigh-frequency rejection. In the communication channel 604 of FIG. 6 b abackgate terminal of PMOS transistor T21 is connected to the (floating)voltage level +fl. The extra high-voltage island is avoided at the costof increased threshold voltage of T21 when T1 is activated. Node Out1does not get as close to the voltage level −fl anymore as in theembodiment 602 of FIG. 6 a. The widths and lengths of T4 and T5 need tobe adapted to still make sure that the output node Out2 is pulled high,which requires an even weaker NMOS T4 and even stronger PMOS T5.

In the circuit of FIG. 6 c a further embodiment 606 of the communicationchannel is depicted. Resistor R11 of the embodiment 604 of FIG. 6 b hasbeen replaced by a PMOS transistor T3 of which the gate is connected tothe (floating) voltage level −fl. Transistor T3 acts as a non-linearresistance. Resistances use a relatively large area of the semiconductordevice, while the transistor T3 may be manufactured at a much smallersize.

Referring to FIG. 1 b, it is to be noted that the reference voltage 128which is provided by the bi-directional switch and which is received onthe reference voltage input terminal 126 may show fast and relativelylarge voltage swings. If the bi-directional switch is implemented as isshown in FIG. 2 a, the reference voltage 128 is obtained from the commonsource s of the NMOS transistors M1 and M2, and therefore the referencevoltage 128 is directly related to the signal that is transmitted by thebi-directional switch. Especially, in for example medical stimulators,the signals which are transmitted through the bi-directional switch mayfollow a wave pattern which has a relatively large amplitude. Thus, whenthe energy storage element is in a floating state, the voltage +fl ofthe first terminal and the voltage −fl of the second terminal may varyrelatively quickly and may have large voltage swings. If a latch is usedto memorize the state of the bi-directional witch, as for example shownin FIG. 2 a, and if the latch is switched with a set and reset signalwhich is provided by a communication channel, which is, for example,shown in FIG. 5 b, the voltages of the set and reset signal that areprovided to the latch may suddenly drop or rise simultaneously. Thisshould not lead to unwanted changes of the state of the latch and thusof state of the bidirectional switch. It is therefore advantageous, asshown in FIG. 7 a, to equip the control circuit with an XOR circuitry702 if a NAND latch 704 is used in the control circuit. If the latch isan NOR latch 708, additional circuitry 706 comprising XNOR gates may beprovided in between the communication channel and the latch of thecontrol circuit, as shown in FIG. 7 b. In both circuitries of FIG. 7 aand FIG. 7 b, whenever both input signals OutSNotFl and OutRNotFlsimultaneously drop or rise, the logic levels of the signals provided tothe NAND latch 704 or the NOR latch 708 do not change. If only one ofthe input signals OutSNotFl and OutRNotFl increases or decreases, one ofthe logic levels of the signals that are provided to the NAND latch 704or the NOR latch 708 changes. It is to be noted that in FIG. 7 a andFIG. 7 b the voltage rails +fl and −fl are shown, which are coupled tothe first terminal and the second terminal, respectively, whichindicates that the XOR circuitry 702, the NAND latch 704, the XNORcircuitry 706 and the NOR latch 708 receive the supply voltage from thevoltage rails +fl and −fl. Thus, they receive a floating supply voltagewhen the energy storage element is in the floating state.

FIG. 8 shows an embodiment of an additional circuit which is comprisedby the control circuit 108 and is coupled in between the latch of thecontrol circuit 108 and the bi-directional switch 132. In thisembodiment, the reference voltage 128 is coupled to the control circuit108. The additional circuit receives a signal from the latch whichindicates the on state or the off state of the bi-directional switch.This signal is fed to a first inverter 802 which comprises transistorT₈₁ and T₈₂ and is fed to a second inverter 804 comprising transistorsT₈₃ and T₈₄ which is coupled in series with a third inverter 806comprising transistors T₈₅ and T₈₆. The output of the first inverter 802provides the control voltage 124 to the control terminal 130 of thebi-directional switch and the output of the third inverter 806 iscoupled to the reference voltage output terminal 142 of thebi-directional switch. Thus, the voltage difference between the controlterminal 130 and the reference voltage output terminal 142 is, dependingon the state of the latch, (+fl-−fl) or -(+fl-−fl). If this voltagedifference is positive, the bi-directional switch 132 is controlled tobe in the on state, if the voltage difference is negative, thebi-directional switch 132 is controlled to be in the off state.

The third inverter 806 connects the reference voltage with the(floating) voltage level of the first terminal +fl or the voltage levelof the second terminal −fl. Thus, the voltage level of the firstterminal +fl or the voltage level of the second terminal −fl issubstantially equal to the reference voltage 128, and thus is the otherone of the voltage levels +fl or −fl and also relates to the referencevoltage 128. The control voltage 124 is, depending on the state of thefirst inverter 802, equal to one of the voltage levels or +fl or −fland, thus, the generated control voltage 124 is related to the referencevoltage 128.

It is to be noted that in the configuration of FIG. 8, instead ofconnecting the common gate g to the control terminal 130, the commonsource s may be connected to the control terminal 130, and consequentlythe common gate g may be connected to the reference voltage outputterminal 142. In the configuration of FIG. 8 it is only important thatthe difference voltage between the common gate g and the common source sis in the on state of the bi-directional switch positive and in the offstage of the bi-directional switch negative. If the common gate and thecommon source are connected differently as discussed in this paragraph,the OutNot output terminal of the latch has to be connected to theadditional circuitry instead of the Out output terminal. FIG. 9 showsanother embodiment of the bi-directional switch 132. The bi-directionalmain current path is in between the drain d1 of NMOS transistor M1 anddrain d2 of NMOS transistor M2. The bi-directional switch 132 has twoadditional input terminals, namely terminal 902 which receives a voltagelevel V_(max) which is higher than all the voltages which possibly occurin the main current path between d1 and d2, and a terminal 904 whichreceives a voltage level V_(min) which is lower than all the voltageswhich possibly occur in the main current path between d1 and d2. In apractical embodiment, V_(min) is the voltage of the substrate of thesemiconductor device in which the bi-directional switch is manufactured.A series arrangement of an NMOS transistor M3 and a PMOS transistor M4that have a common source s₂ and a common gate g₂ is arranged in betweenthe terminal 902 and the terminal 904. The NMOS M3 and the PMOS M4 forma class-B circuit. Both transistors are enhancement MOSTs such that theycannot conduct simultaneously (class-B operation). The common source s₂is connected to the reference voltage output terminal 142. The commonsource g₂ is connected to the common source s₁ of the NMOS transistorsM1 and M2. The function of M3 and M4 is that the reference voltage 128on the reference voltage output terminal gets a voltage level which isclose to the voltage level of the common source s₁. The referencevoltage 128 differs from the voltage level of the common source s₁ withan amount which is in a range between the threshold voltage of the NMOStransistor M3 and the threshold voltage of PMOS transistor M4. Namely,as soon as the reference voltage 128 is higher than the voltage of thecommon source s₁ (which equals the voltage of the common gate g₂), PMOStransistor M4 conducts until the level of the reference voltage 128 isalmost equal to the voltage of the common source if the referencevoltage 128 is lower than the voltage of the common source s₁, NMOStransistor M3 conducts until the level of the reference voltage 128 isalmost equal to the voltage of the common source s₁.

FIG. 10 schematically shows the embodiment of FIG. 9 wherein theparasitic (pn-junctions) diodes Dpar₁ . . . Dpar₄ from the substrate ofthe semiconductor device to terminals of the transistors M1 . . . M4,respectively, are drawn.

In the discussion which follows in this paragraph, we assume thattransistors M3 and M4 are not present and that the common source s₁ iscoupled to the reference voltage output terminal 142. As discussedbefore, if the communication circuits 502, 504, 602, 604, 606 of FIGS. 5a, 5 b, 6 a, 6 b, 6 c communicate a set or a reset signal to a voltagelevel related to the voltage levels +fl and/or −fl, a current flowsthrough the communication circuits from the voltage level +fl to thesubstrate of the semiconductor device on which the control circuitry(and probably the bi-directional switch is manufactured. The currentsonly flow for short periods of time. Further, currents always flowclosed loops, and thus a part of the currents flowing through thecommunication channel flows from the substrate back via the parasiticdiodes Dpar₁ and/or Dpar₂ to the I/O terminals of the bi-directionalswitch, especially when the bi-directional main current path is in theoff-state. If the bi-directional main current path is in the on-state,the small currents flow through the bi-directional main current path viathe circuitry which is connected to the I/O terminals of thebi-directional switch. This means that, for short periods of time, theI/O terminals of the bi-directional switch may receive a current whichdoes not relate to the signal that has to be transmitted via thebi-directional switch. The I/O terminals of the bi-directional switchmay, for example, be coupled to measurement circuits and themeasurements may be disturbed by these currents.

If, as drawn in FIG. 10, MOS transistors M3 and M4 are present, theshort current pulses flow in a different path. If the bi-directionalswitch transistors M1 and M2 are conductive, the pulses flow via theenergy storage element, via transistor T₈₆ of inverter 806 of FIG. 8 tothe reference voltage output terminal 142 and subsequently via Dpar₄. Inthe case that M3 conducts, the current loop is closed via the conductivechannel of M3. If M1 and M2 are non-conductive, the current loop isclosed via the transistors T₈₅ of inverter 806 of FIG. 8, via thereference voltage output terminal 142 and via the diode Dpar₄. Also inthe case that M1 and M2 are non-conductive, and M3 conducts, the currentloop is closed via the conductive channel of M3. Thus, the embodiment ofFIG. 10 is advantageous because it prevents the disturbance of thesignals on the I/O terminals of the bi-directional switch.

FIG. 11 schematically shows an embodiment of a bi-directional switch1104 system according to the second aspect of the invention. Thebi-directional switch system 1004 has a bi-directional main current path1112 between a first I/O terminal 1106 and a second I/O terminal 1114.At least one semiconductor switch 1110 is provided in the bi-directionalmain current path 1112. The on and off state of the semiconductor switch1110 is controlled by a control circuitry 1102. Embodiments of thesemiconductor switch 1110 and of the control circuitry 1102 arediscussed previously.

FIG. 12 schematically shows an embodiment of a switching matrix 1200.The switching matrix 1200 comprises a plurality of columns C₁ to C_(N)and a plurality of rows R₁ to R_(M). A bi-directional switch system 1202is provided at at least one junction between a column C_(i) and a rowR_(j). In the example of FIG. 12 the bi-directional switch system 1202is provided at a junction formed by row R₃ and column C₃. Thebi-directional switch system 1202 comprises a semiconductor switch 1206and the on and off state of the semiconductor switch 1206 is controlledby a control circuitry 1204. Embodiments of the semiconductor switch1206 and of the control circuitry 1204 are discussed previously. Itshould be noted that in an embodiment all the junction points of thematrix each have a bi-directional switch with a control circuitry.

FIG. 13 schematically shows a medical stimulator 1300 according to thefourth aspect of the invention. The medical stimulator 1300 has aplurality of electrodes 1310 . . . 131 n which may be brought in contactwith the body of a person to simulate, for examples, muscles of theperson, or in another example, to provide deep brain stimulation to theperson. The signal that is provided via the electrodes to the person maybe selected by the user or a medical expert with a selection button1302. Depending on the selection, a signal generator 1306 generates asignal. The signal generated by the signal generator 1306 may beconnected to one of the electrodes 1310 . . . 131 n via a bi-directionalswitch. The medical stimulator 1300 comprises at least onebi-directional switch system which comprises at least one semiconductorswitch 1308 in a bi-directional main current path of the bi-directionalswitch system. The on and off state of the bi-directional switch iscontrolled by a control circuitry 1304. Embodiments of the semiconductorswitch 1308 and of the control circuitry 1304 are discussed previously.In another embodiment, the medical stimulator 1300 comprises a switchingmatrix according to the third aspect of the invention.

FIG. 14 schematically shows an embodiment of the method 1400 ofcontrolling a bi-directional switch according to the fifth aspect of theinvention. The bi-directional switch has a control terminal forreceiving a control voltage to control an on and off state of thebi-directional switch and at least one semiconductor switch in abi-directional main current path. The method comprises a first step ofcoupling 1402 by means of a coupling means an energy storage element toa supply voltage only when the bi-directional switch is in the off statefor charging the energy storage element. In another step the methodreceives 1404 power from the energy storage element in a controlcircuit. In a further step the method supplies 1406 by means of thecontrol circuit the control voltage having a voltage level beingindependent of the supply voltage when the energy storage clement is notcoupled to the supply voltage.

It is to be noted that the control circuitry according to the firstaspect of the invention, the bi-directional switch system, a switchingmatrix, or the method according to the fifth aspect of the invention maybe used in a plurality of applications. A first example are medicalimplants which include a cross point switch matrix to couple internalcircuitry to external probes both for stimulation and/or recording, suchas Deep Brain Stimulators or Pace Makers. In a second example, intelephony, a circuitry near or within the Subscriber Line InterfaceCircuit couples the subscriber telephone line to the internal circuitryof a telephone exchange using for example a cross-point switch matrix.In a third example, integrated display drivers use supply voltages of afew tens of volts, which may be switched via a bi-directional maincurrent path of a bi-directional switch. In a fourth example, across-point switch matrix could be used to couple various piezo elementsto piezo drivers integrated in a CMOS technology. In a fifth example,LEDs for lighting applications are often arranged in series to form LEDstrings and the voltage to supply power to the LED strings may beswitched via a bi-directional switch system. In a sixth example,advanced power supply conversion systems require bi-directional switchesfor increased functionality and/or efficiency.

It should be noted that the above-mentioned embodiments illustraterather than limit the invention, and that those skilled in the art willbe able to design many alternative embodiments without departing fromthe scope of the appended claims.

In the claims, any reference signs placed between parentheses shall notbe construed as limiting the claim. Use of the verb “comprise” and itsconjugations does not exclude the presence of elements or steps otherthan those stated in a claim. The article “a” or “an” preceding anelement does not exclude the presence of a plurality of such elements.The invention may be implemented by means of hardware comprising severaldistinct elements, and by means of a suitably programmed computer. Inthe device claim enumerating several means, several of these means maybe embodied by one and the same item of hardware. The mere fact thatcertain measures are recited in mutually different dependent claims doesnot indicate that a combination of these measures cannot be used toadvantage.

1. A control circuitry (134, 1102, 1204, 1304) for controlling abi-directional switch (132, 212, 220) having a control terminal (130)for receiving a control voltage to control an on state and an off stateof the bi-directional (132, 212, 220) and at least one semiconductorswitch (143, M1, M2, M10, M20, 1110, 1206, 1308) in a bi-directionalmain current path (144, 1112), the control circuitry (134, 1102, 1204,1304) comprises: an energy storage element (102, Cstor), coupling means(101) for coupling the energy storage element (102, Cstor) to a supplyvoltage for charging the energy storage element (102, Cstor), and acontrol circuit (108,208, 222) configured for receiving power from theenergy storage element (102, Cstor) and configured for supplying thecontrol voltage having a voltage level being independent of the supplyvoltage when the energy storage element (102, Cstor) is not coupled tothe supply voltage, wherein the coupling means (101) is configured foronly coupling the energy storage element (102, Cstor) to the supplyvoltage when the bi-directional switch (132, 212, 220) is in the offstate.
 2. A control circuitry (134, 1102, 1204, 1304) according to claim1 further comprising a reference voltage input terminal (126) forreceiving a reference voltage, wherein the bi-directional switch (132,212, 220) further comprises a reference voltage output terminal (130)for providing the reference voltage indicating to which voltage levelthe control voltage on the control terminal has to be defined to enableswitching of the bi-directional switch, wherein the energy storageelement (102, Cstor) has a first terminal (104) and a second terminal(136), wherein the coupling means (101) comprises i) a first switch (S1)arranged between the first terminal (104) and a first supply voltageterminal (112) for receiving a first supply voltage, ii) a second switch(S2) arranged between the second terminal (136) and a second supplyvoltage terminal (120) for receiving a second supply voltage, and iii) afurther control circuit (116, 210, 216, 404, 408) for controlling atleast one of the first switch (S1) and the second switch (S2) to be openor closed and being configured for only closing at least one of thefirst switch (S1) and the second switch (S2) when the bi-directionalmain current path (144, 1112) of the bi-directional switch (132, 212,220) is in the off state, wherein, when both the first switch (S1) andthe second switch (S2) are closed, the energy storage element (102,Cstor) is charged to a voltage being a difference between the firstsupply voltage and the second supply voltage, and wherein, when both thefirst switch (S1) and the second switch (S2) are open, the voltages ofthe first terminal (104) and the second terminal (136) are floating toobtain a floating state of the energy storage element (102, Cstor), andwherein the control circuit (108,208, 222) comprises power supplyterminals (106, 138) being coupled between the first terminal (104) andsecond terminal (136) to receive power supply energy from the energystorage element (102, Cstor), wherein the control voltage is generatedin a floating manner when the energy storage element (102, Cstor) is inthe floating state.
 3. A control circuitry (134, 1102, 1204, 1304)according to claim 2, wherein the control circuit (108,208, 222)comprises a latch (206, 224, 704, 708) for memorizing the on state orthe off state of the bi-directional switch (132, 212, 220) and forsupplying the control voltage according to the memorized state.
 4. Acontrol circuitry (134, 1102, 1204, 1304) according to claim 2, whereinthe control circuit (108,208, 222) comprises an input terminal (T1ctrl,Ins, InR) in receiving a switch control signal which indicates arequired on or off state of the bi-directional switch.
 5. A controlcircuit (134, 1102, 1204, 1304) according to claim 3, wherein thecontrol circuit (108,208, 222) is coupled to at least one of the firstsupply voltage terminal (112) and to the second supply voltage terminal(120), the input terminal is configured to receive the switch controlsignal which relates to at least one of the first supply voltage and thesecond supply voltage, and the control circuit (108,208, 222) comprisesa communication channel (204, 218, 502, 504, 602, 604, 606) forcommunicating the bi-directional switch control signal to a floatingcontrol signal having a voltage related to the voltage of the firstterminal and/or of the second terminal.
 6. A control circuitry (134,1102, 1204, 1304) according to claims 2 and 5, wherein the latch (206,224, 704, 708) is arranged to store the on state of the bi-directionalswitch (132, 212, 220) in response to receiving a set signal and the offstate of the bi-directional switch (132, 212, 220) in response toreceiving a reset signal, the bi-directional switch control signalcomprises a set sub-signal and a reset sub-signal, and the communicationchannel (204, 218, 502, 504, 602, 604, 606) communicates the setsub-signal and the reset sub-signal to the latch (206, 224, 704, 708).7. A control circuitry (134, 1102, 1204, 1304) according to claim 1,wherein the energy storage element (102, Cstor) is a storage capacitor(Cstor) manufactured on basis of a MOS transistor (302, 304) of whichthe drain, the source and the backgate are electrically connected toeach other, together forming a first electrode of the storage capacitor(Cstor), and wherein the gate of the MOS transistor (302, 304) forms thesecond electrode of the storage capacitor (Cstor).
 8. A controlcircuitry (134, 1102, 1204, 1304) according to claim 2, wherein thefirst switch (S1) or the second switch (S2) is a bootstrap diode(D_(S1))), and the other one of the first switch (S1) and the secondswitch (S2) is a MOS transistor (T_(S2))), and wherein a conducting or anon-conducting state of the MOS transistor is controlled by the furthercontrol circuit (116, 210, 216, 404, 408).
 9. A control circuitry (134,1102, 1204, 1304) according to claim 2, wherein the first switch (S1) isa first MOS transistor (T_(S1)), and the second switch (S2) is a secondMOS transistor (T_(S2)), wherein a conducting or a non-conducting stateof the first MOS transistor and a conducting or a non-conducting stateof the second MOS transistor is controlled by the further controlcircuit (116, 210, 216, 404, 408).
 10. A bi-directional switch system(1104) comprising a bi-directional switch (132, 212, 220) and thecontrol circuitry (1102) according to claim
 1. 11. A bi-directionalswitch system (1104) according to claim 10 wherein the bi-directionalswitch (132, 212, 220) comprises a bi-directional main current path(144, 1112) between a first I/O terminal and a second I/O terminal, andcomprising a first MOS transistor (M1) and a second MOS transistor (M2)in the main current path (144, 1112), wherein the first MOS transistor(M1) and the second MOS transistor (M2) have a common source (s, s1) anda common gate (g, g1), a drain (d1) of the first MOS transistor (M1) iscoupled to the fist I/O terminal, a drain (d2) of the second MOStransistor (M2) is coupled to the second I/O terminal, the common gate(g, g1) is coupled to a control terminal (130) of the bi-directionalswitch (132, 212, 220).
 12. A bi-directional switch system (1104)according to claim 11, wherein the common source (s, s1) is coupled to areference voltage output terminal (130) of the bi-directional switch(132, 212, 220).
 13. A switching matrix (1200) comprising at least onebi-directional switch system (1202) as claimed in claim 10 at at leastone junction point of the switching matrix.
 14. A medical stimulator(1300) for providing electrical stimulation signals and the medicalstimulator (1300) comprising at least one bi-directional switch system(1104) according to claim
 10. 15. A method (1400) of controlling abi-directional switch having a control terminal for receiving a controlvoltage to control an on and off state of the bi-directional switch andat least one semiconductor switch in a bi-directional main current path,the method comprises the steps of coupling (1402) an energy storageelement to a supply voltage only when the bi-directional switch is inthe off state for charging the energy storage element, receiving (1404)power from the energy storage element, supplying (1406) the controlvoltage having a voltage level being independent of the supply voltagewhen the energy storage element is not coupled to the supply voltage.